This disclosure relates generally to seismic exploration, with particular applicability to marine seismic exploration.
In seismic exploration, seismic data may be acquired by imparting acoustic energy into the earth near its surface, and detecting acoustic energy that is reflected from boundaries between different layers of a subsurface rock formation. Acoustic energy is reflected when there is a difference in acoustic impedance between adjacent layers to a boundary. Signals representing the detected acoustic energy are interpreted to identify potential subsurface structures and composition of the subsurface rock formation, thereby to aid in the identification and production of hydrocarbons.
In marine seismic exploration, a seismic energy source, such as an air gun, marine vibrator, or arrays of airguns and/or marine vibrators, is typically used to impart the acoustic energy into the formations below the bottom of the water. The seismic energy source is actuated at a selected depth in the water, typically while the seismic energy source is being towed by a vessel. The same or a different vessel tows one or more seismic sensor cables, called streamers, in the water. Generally the streamer extends behind the vessel along the direction in which the streamer is towed. Typically, a streamer includes a plurality of seismic sensors, such as hydrophones, for example, disposed on the cable at spaced apart, known positions along the cable. Hydrophones are seismic sensors that generate an optical or electrical signal corresponding to the pressure of the water or the time gradient of pressure in the water. Seismic sensors may also be located at or near the bottom of the body of water, on one or more ocean bottom cables or a plurality of nodes. The vessel that tows the one or more streamers typically includes recording equipment to make a record, indexed with respect to time, of the signals generated by the seismic sensors in response to the detected acoustic energy. The record of signals may be processed to infer structures of and compositions of the earth formations below the locations at which the seismic survey is performed.
While the invention will be described in connection with one or more embodiments, it will be understood that the invention is not limited to these. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents that may be included within the scope of the invention, as defined by the appended claims.